1. Field of the Invention
This document relates to a shift register and a display device using the same.
2. Discussion of the Related Art
Recently, various flat panel display devices have been developed that have reduced weight and bulk and are thus capable of overcoming the disadvantages of a cathode ray tube (CRT) display.
A scan driving circuit used in the flat panel display generally sequentially supplies scan pluses for scan lines using a shift register.
The shift register of the scan driving circuit includes, as shown in FIG. 1, stages ST(n−1) to ST(n+2) each consisting of thin film transistors (TFTs). The stages are connected to each other in cascade to generate outputs Vout(n−1) to Vout(n+2). The reference numerals “C1 to C4” in FIG. 1 denote four-phase clocks provided to the stages.
Each of the stages ST(n−1) to ST(n+2) includes a Q node for controlling a pull-up transistor, and a Q bar (QB) node for controlling a pull-down transistor. In addition, each of the stages ST(n−1) to ST(n+2) includes switch circuits which charge and discharge the Q node and QB node in response to a carry signal output from a previous stage, a carry signal output from a next stage, and the clock signals C1 to C4.
The outputs Vout(n−1) to Vout(n+2) from the stages ST(n−1) to ST(n+2) of the shift register are used as scan pluses applied to the scan lines of the display device and the carry signals applied to the previous and next stages. Thus, when, as shown in FIG. 1, due to conductive particles CP mixed in the course of a manufacturing process or a poor pattern, the scan lines connected to output nodes of the stages ST(n−1) to ST(n+2) are short-circuited to other scan lines or DC voltage sources VDD and VSS, the carry signals are not transmitted and thus the shift register is wrongly operated. For example, as shown in FIG. 1, when an n-th (where n is a positive integer) scan line connected to the output node of the n-th stage ST(n) is short-circuited to a (n+1)-th scan line connected to the output node of the (n+1)-th stage ST(n+1), the stages following the n-th stage ST(n) is not operated normally.
Meanwhile, a scan direction in the shift register is required to vary depending on a panel structure or a driving method of the display device. Therefore, the shift register preferably has a function capable of changing a shift direction.